The present invention relates to magnetostrictive elements and the use thereof.
Magnetostrictive materials are known. They are understood to be materials whose dimensions change in the presence of a magnetic field, or which generate magnetic fields in the event of changes in their dimensions.
The magnetostrictive effect is like the piezoelectric effect, which causes changes in the dimensions of the material as a result of the presence of an electric field. With the piezoelectric effect, very high electric field strengths and very high voltages, on the order of several kilovolts, must typically be used in order to achieve significant changes in dimension. In contrast, magnetostrictive materials are known with which comparatively low voltages need to be used in order to achieve the desired changes in dimension. Such a material is known under the name of Terfenol-D; it is an alloy of iron, terbium and dysprosium.
Magnetostrictive materials are described, for example, in documents EP-A-361,969, WO-A-00/33,324, U.S. Pat. No. 6,273,965 and U.S. Pat. No. 5,223,046.
Magnetostrictive elastomer materials are also already known (cf. Midé Technology Corporation, Magnetostrictive Elastomers, for example, www.mide.com). Details of their composition are not provided in the document.
Furthermore, elastomer foams containing magnetic particles are also known.
JP-A-2002/278,424 discloses a foamed polymer material containing magnetic powder. This is used for sealing photocopiers, in order to prevent the escape of toner. Possible polymers are elastomers, such as ethylene-propylene elastomers.
JP-A-03/122,139 discloses magnetized rubber masses for the production of crosslinked foams. These are used for soundproofing and for absorbing vibrations.
JP-A-58/533,928 discloses flexible cellular elastomers containing metal powder. These are used for shielding against radiation.
None of these documents discloses the use of elastomer foams utilizing the magnetostrictive effect, for example the use of such foams as actuators, adaptive dampers or sensors for changes in material dimensions.
It has now been found that porous polymers containing ferromagnetic particles demonstrate a significantly enhanced magnetostrictive effect in comparison with the corresponding compact polymer materials.